Hello friends welcome to engineering Panda family in this video I'm going to explain you energy bands as well as I'll explain you how classification of solid material is there with respect to energy bands so first of all I'll explain you energy bands in material basically there are two categories of band available with material in terms of energy bands valence band and conduction band see valence band balance band that is associated with valence electrons and conduction band that is associated with free electrons so first of all you need to understand what is the meaning of valence electrons see valence electrons are the electrons which are bounded in its atomic structure like as if you talk about one silicon atom over here then you can observe in the silicon atom with first orbit we are having two electrons with second orbit we are having eight electrons with outermost orbit we are having four electrons so these are the electrons which are bounded in its atomic structure If You observe atomic structure of silicon then there are covalent bonds by which these electrons are connected with each other so the electrons which are connected in its atomic structure those are valence electrons and the electrons which are not connected in its atomic structure those are free electrons so here see valence electrons that will Define valence band and free electrons that will Define conduction band so first of all you should be having idea about what is valence electrons see valence electrons are connected in its atomic structure and free electrons are not connected in its atomic structure so free electrons only participates in flow of current so whenever you apply potential difference in between two terminal of material then there is a possibility of flow of current and that flow of current is possible due to free electrons only always remember this valence electrons does not participate in flow of current right so let me explain you how valence band and conduction band is there now balance band energy will be always low why it will be always lower the reason is valence band is associated with valence electrons and valence electrons are bounded in a bond of atomic structure as those electrons are bounded those electrons are having lower energy and because of that balance band will be having low energy valence electrons are bounded in atomic structure so valence electrons does not participate in flow of current while when you talk about conduction band conduction band is having higher energy the reason is conduction band is associated with three electrons and three electrons are not bounded in atomic structure so free electrons only participate in flow of current so first of all you should know in structure there are two types of electrons right the electrons which are bounded in the structure those are valence electrons energy associated with valence electrons is valence band that energy will be low free electrons are not bounded in the structure energy associated with free electrons will be there in conduction band and that will be having higher energy right now when you talk about energy then here you see I have drawn energy band diagram so here conduction band energy that is high I have told you why the reason is conduction band energy that is associated with free electrons valence band energy that will be low why the reason is balance band energy that is associated with the electrons which are bounded in the structure Gap in between conduction band and Valence band is referred as forbidden energy gap now what is the meaning of forbidden energy see in Balance band there will be electrons let me draw some electrons over here see in valence band there are few electrons right now see to have flow of current if I want to move this electrons in conduction band then how much energy that I need to give it to this electron that is what forbidden energy gap see if you have a material in which there is no free there is no free electron then is it possible that there can be flow of current if there is no free electron then there cannot be flow of current but if you increase potential difference in between material then this electrons will gain energy and as if this electrons jumps into the conduction band means now those electrons are getting free then those electrons which are there in conduction band they can only participate in slow of current so here you see this atomic structure that is having electrons which are valence electrons so these electrons cannot participate in flow of current but as if I give energy to electrons like as if I give energy to this electron and as if I make it free as if I make it free right then this electron will go in conduction band and that electron can participate in flow of current so to give so to give energy to electron here we need to give some electric field or we can give some potential difference or you can provide heat as well there are multiple ways by which we can give energy to electrons either you give heat to material or you can provide potential difference in between material as well as you can provide High electric field to material by which you can transfer this valence electron into conduction band and you can make it free and this Gap is referred as forbidden energy gap now let me explain you how classification of solid material is there probably I think you might be having idea about what is what is Conductor semiconductor and insulator right still let me tell you see in conductor we are having higher conductivity means easily we can flow current inside conductor in semiconductor you will have to give more energy for a flow of current while in insulator it is bit difficult to flow current why the reason is forbidden energy gap that is very high If You observe energy band diagram over here you see with conductor conduction band and Valence band that is overlapped over each other as it is overlapped over each other easily flow of current will happen by applying potential difference as if you talk about semiconductor then forbidden energy gap in between conduction band and Valence band that is bit low silicon it is around 1.1 electron volt right so with silicon material if you give 1.1 electron volt energy to one electron then that electron will jump from valence band to conduction band and those electrons can participate into flow of current but if you talk about insulator so in that if You observe here forbidden energy gap that is very high it is greater than 6 electron volt so as forbidden energy gap is very high in insulator there will be no flow of current even if you apply some potential difference in between two terminal of material here there are few parameters that you need to understand and I have seen see this parameters that frequently comes in competitive examination so you should remember those parameters right like how conductivity is there so with conductor High conductivity will be there within with semiconductor moderate conductivity will be there and with insulator low conductivity will be there see with conductor conductivity that is represented by Sigma and that will be greater than 10 to the power 7 per ohm meter see this Sigma that is having unit which is per ohm meter remember this Sigma is having unit that is per ohm meter and that will be greater than 10 to the power 7 if you talk about semiconductor material then this Sigma conductivity that will be there somewhere in between 10 to the power 4 to 10 to the power minus 6 right and for insulator that conductivity will be very low that will be the in terms of 10 to the power minus 10 per ohm meter So based on conductivity also you can classify those materials based on resistivity also we can classify the material now what is the relation in between conductivity and resistivity see conductivity is inversely proportional to resistivity so Sigma that is inversely proportional to rho mean Sigma is proportional to 1 by rho so you can observe here unit is ohometer with conductivity unit is per ohm meter with resistivity unit is ohm beta right so rho that will be lower than 10 to the power minus 7 for conductor so it will be having lower resistivity moderate resistivity will be there with semiconductor material right and high resistivity that will be there with insulating materials some examples that I have written over here like with conductor we can have copper aluminum those are not ideal conductor but you can say those are conductors that is having good conductivity for Semiconductor silicon and germanium that people are widely using nowadays right now if you talk about semiconductor chips then that is made up of silicon material only and as if you talk about insulating material then Mica would right so those are the real life examples of insulating material so here there are few basic points that you need to note down see first of all what is the meaning of valence band and conduction band and what is forbidden energy gap balance band that is associated with valence electrons and valence electrons are there in atomic structure as per some bonds right and conduction band that is associated with free electrons three electrons are free those are not connected in atomic structure so those electrons which are free they can participate in flow of current valence band will be always having lower energy conduction band will be always having higher energy right and here one example that I have given over here and to understand materials based on energy band diagram you should note down see with insulator forbidden energy gap which is a gap in between conduction band and balance band that will be very high that will be probably greater than 6 electron volt for Semiconductor material it will be a bit lower compared to this I have given one example of silicon material where forbidden energy gap that is 1.1 electron volt right so that is how things are there I hope now your Basics are cleared still if anything that would like to share please note it down in comment section I'll be happy to help you thank you so much for watching this video